HVJ is a kind of mouse pneumonia viruses and is not infectious to human. It has two types of glycoproteins (F and HN) on its cell-fusing viral outer membrane, and the proteins have the ability to fuse two types of cells (cell fusion). In recent years, a technique using the envelope of HVJ as a vector (HVJ envelope vector) was developed and has been commercialized (Patent Literature 1). The envelope of HVJ is used as the HVJ envelope vector after removing the genomic RNA of HVJ. A desired foreign gene is encapsulated in the envelope and the virus is infected to cultured cells or an organ so as to transfect the desired gene into the cells. Since the genomic RNA of the virus has been removed, the HVJ envelope is highly safe. Since the envelope has an ability to fuse cells, the efficiency of transfection into the cell is high. A large amount of foreign genes can be encapsulated, and the host spectrum of the virus is wide. Therefore, it is expected that the vector will be more and more widely used as a tool for analyzing gene function and as a vector for gene therapy.
Mass production of HVJ is conventionally carried out by inoculating HVJ to chicken eggs and growing the virus (see Virus Experimental Protocols, Medical View Co., Ltd., 1995, 68-78). However, with this method, there is a possibility that a highly immunogenic protein such as egg white albumin or the like or other impurities originated from the chicken egg may be contaminated in the recovered HVJ. Therefore, WHO recommends not to use chicken eggs but to use human cultured cells. When chicken eggs are used as a host, the inoculation operation of the virus and the recovery operation of the virus after growth thereof are complicated, so that the throughput is limited. To solve these problems, it is thought to grow HVJ using mammalian cultured cells in place of chicken eggs. Since mammals are the proper hosts of HVJ, HVJ can grow in various mammalian cells. However, no mammalian cultured cells which are suited for the mass production of HVJ are known.    Patent Literature 1: JP 2001-286282 A    Non-patent Literature 1: Virus Experimental Protocols, Medical View Co., Ltd., 1995, 68-78